Photochem

Porphyrins play important roles in biological systems including oxygen transport and catalysis. Due to their tetrapyrrole core structure, they exhibit exceptional photophysical and electrochemical properties and find many applications in both technical and life science fields, including photodynamic therapy and neurosurgery. The irradiation of porphyrins may cause modifications to their molecular structure or their degradation. Such photobleaching processes potentially affect the success and sensitivity of photosensitizer applications. While there have been many studies using fluorescence spectroscopy to investigate this phenomenon, reports about analytically validated structures of photoproducts are scarce. It is, however, necessary to know the individual contributions of different molecules to the fluorescence signal in order to evaluate it correctly. This review provides a summary of the current state of knowledge in this respect, discussing especially the validated hydroxyaldehyde and formyl photo-oxidation products of protoporphyrin IX. Full article

In this work, we report the fabrication of CuI@g-C₃N₄/MoS₂ thin films by the thermal evaporation of Cu films and their conversion into hybrid films by a simple wet chemical method. Compared to pure CuI, CuI@g-C₃N₄/MoS₂ shows enhanced absorption near the UV region, which improves its DC photoconductivity. The conductivity of the films is enhanced by the addition of g-C₃N₄/MoS₂, which is distributed on the surface of the CuI film. The band gap of the films red-shifts upon adding g-C₃N₄/MoS₂. We evaluate this material’s potential application as a photodetector and in photocatalysis by evaluating its photoelectrochemical properties using impedance spectroscopy measurements, cyclic voltammetry, and DC photoresponse measurements. We find that upon the addition of g-C₃N₄/MoS₂, the conductivity of the films is increased, as evidenced by the time-dependent photo amperometry measurements. Also, a higher DC photoresponse is observed upon increasing the concentration of MoS₂. This work marks the first time a hybrid CuI@g-C₃N₄/MoS₂ film and its photoelectrochemical characteristics have ever been reported. Full article

Chemically identical chlorophyll (Chl) molecules undergo conformational changes when they are embedded in a protein matrix. The conformational changes will modulate their absorption spectra to meet the need for programmed excitation energy transfer or electron transfer. To interpret spectroscopic data using the knowledge of pigment–protein interactions requires a single pigment embedded in one polypeptide matrix. Unfortunately, most of the known photosynthetic systems contain a set of multiple pigments in each protein subunit. This makes it complicated to interpret spectroscopic data using structural data due to the potential overlapping spectra of two or more pigments. Chl–protein interactions have not been systematically studied to answer three fundamental questions: (i) What are the structural characteristics and commonly shared substructures of different types of Chl molecules (e.g., Chl a, b, c, d, and f)? (ii) How many structural groups can Chl molecules be divided into and how are different structural groups influenced by their surrounding environments? (iii) What are the structural characteristics of pigment surrounding environments? Having no clear answers to the unresolved questions is probably due to a lack of computational methods for quantifying conformational changes in individual Chls and individual surrounding amino acids. The first version of the Triangular Spatial Relationship (TSR)-based method was developed for comparing protein 3D structures. The input data for the TSR-based method are experimentally determined 3D structures from the Protein Data Bank (PDB). In this study, we take advantage of the 3D structures of Chl-binding proteins deposited in the PDB and the TSR-based method to systematically investigate the 3D structures of various types of Chls and their protein environments. The key contributions of this study can be summarized as follows: (i) Specific structural characteristics of Chl d and f were identified and are defined using the TSR keys. (ii) Two and three clusters were found for various types of Chls and Chls a, respectively. The signature structures for distinguishing their corresponding two and three clusters were identified. (iii) Histidine residues were used as an example for revealing structural characteristics of Chl-binding sites. This study provides evidence for the three unresolved questions and builds a structural foundation through quantifying Chl conformations as well as structures of their embedded protein environments for future mechanistic understanding of relationships between Chl–protein interactions and their corresponding spectroscopic data. Full article

We report on the phosphorescence of singlet oxygen photogenerated through a stimulated Raman process. Nanosecond radiation in the green spectral region focused on hexane and carbon tetrachloride induces a Raman transition of the dissolved solvent oxygen molecules towards the singlet oxygen state, producing a Stokes signal in the near-infrared. The excited oxygen relaxes to the ground, emitting an infrared photon at 1272 nm. While the Stokes signal’s wavelength changes with the light’s wavelength, the wavelength of the phosphorescent photon remains unaltered. The result confirms previous reports on the stimulated Raman excitation of singlet oxygen. Full article

Visible-light-responsive silver-phosphate-sensitized fly-ash particles loaded on polyurethane nanofiber (Ag₃PO₄–FA/PU NFs) membrane photocatalysts were prepared by electrospinning followed by an ion-exchange method and characterized with state-of-art techniques. With the assistance of Ag₃PO₄–FA/PU NFs, 98 % of methylene blue (MB) was degraded within 60 min. The combination of FA and Ag₃PO₄ particles provided simultaneous adsorption and degradation of MB in an aqueous solution, resulting in the fast removal of the dye. Also, the Ag₃PO₄–FA/PU NFs exhibited excellent antibacterial performance toward Escherichia coli and Staphylococcus aureus bacteria. Thus, the prepared photocatalyst may provide a potential outcome for environmental remediation, especially wastewater treatment applications. Full article

Astrophysical ices play a crucial role in the chemistry of cold interstellar environments. However, their diverse compositions, temperatures, and grain morphologies pose significant challenges for molecular identification and quantification through infrared observations. We investigate the ability of implicit solvation approaches to capture temperature-dependent infrared spectral features of CO₂ molecules embedded in astrophysical ice analogues, comparing their performance to that of explicit ice models and experimental data. Using DFT calculations and vibrational frequency scaling, we model CO₂ trapped in both amorphous (cold) and crystalline (warm) H₂O ice clusters. The implicit model qualitatively identifies certain trends but fails to reliably capture the magnitude of frequency shifts and band strengths. Explicit models correctly reproduce the gas-to-solid redshifts for both the asymmetric stretch and bending modes; however, neither approach successfully replicates the experimentally observed temperature-dependent trend in the bending mode. While continuum-like methods may be useful as first-order approximations, explicit modelling of the molecular environment is essential for accurately simulating the infrared spectral behaviour of CO₂ in astrophysical ices and for interpreting observational data on ice composition and evolution. Full article

This communication aims to comprehensively elucidate the intricate mechanism governing the interaction between the excited triplet state of 4-Carboxybenzophenone (CB*) and the anionic form of 2-Naphthalene Sulfonate (NpSO₃⁻), employing the 337 nm Nanosecond Laser Flash Photolysis technique for this investigation. When the CB is selectively excited by a 337 nm laser, two primary processes become possible: (i) energy transfer from ³CB* to NpSO₃⁻ and (ii) electron transfer from NpSO₃⁻ to ³CB*. The dynamics of these interactions are explored through experimental observations of transient absorption spectra and the analysis of respective kinetic traces. The primary process dominating in the ³(CB...NpSO₃⁻)* system is identified as triplet energy transfer from excited ³CB* to ³(NpSO₃⁻), as demonstrated by characteristic spectral features observed at 410–420 nm. Comparisons are made with a similar system studied by Yamaji and co-workers, ³(BP^•−...NpO^•)*, revealing differences in the priority of primary process occurrences. These findings contribute to a deeper understanding of the intricate interactions between excited molecules and ground-state donors, aiding in the comprehension of mechanisms governing these reactions. Full article

Atomically precise noble metal nanoclusters protected by ligands are broadly discussed in the literature as a promising new class of materials with many interesting properties. Of those, the most prominent is the characteristic luminescence in the visible and near-infrared light. Within the plethora of conjugates of metal nanoclusters to various protective ligands, protein-enveloped systems present several unique features arising from an interplay of the nanocluster photophysics and the protein chemistry along its macromolecular dynamics. The specific properties of protein–metal nanocluster conjugates underlie various applications of these systems, especially in bioimaging. This review, in contrast to many already published, focuses on protein-protected gold nanoclusters (AuNCs) from the standpoint of the proteinaceous shell which plays a crucial role in the biocompatibility, solubility, and excellent in-solution stability of such nanohybrid complexes. Factors such as the protein’s size, structural rigidity, amino acid composition, electric charge, and the electron donor properties of composite amino acids are discussed. Full article

Biomarker detection is imperative in the realms of modern medicine, biology, and environmental science, owing to the numerous avenues for its application. The recent scientific upsurge in the development of molecules, materials, and mechanisms for such scientific development has garnered considerable attention among scientists. In this connection, excited-state intramolecular proton transfer (ESIPT) properties of photoluminescent compounds provide considerable insights into the designing, development, and detection of biomarkers. ESIPT molecules significantly show a Stokes-shifted emission due to their sensitive nature and unique photophysical properties. Leveraging this photophysical property and tunable nature, several fluorescent probes of this genre can be designed and synthesized for a plethora of application spheres. Schiff bases encompass one such category of functional molecules displaying ESIPT properties, which can be mitigated by adding several other functionalities and desired optical characteristics. The current review article spans the basics of ESIPT properties of certain photoluminescent molecules and also envisages biosensing applications of recently developed imine–functionalized Schiff base molecules with such properties as the prima-foci, along with other applications. Full article

The textile industry is a major contributor to environmental pollution, primarily through the discharge of wastewater loaded with dyes and contaminants that disrupt natural ecosystems. This study aims to develop a hybrid material by functionalizing carbon nanodots (CNDs) with the donor-π-acceptor organic dye L1 via amide coupling. By chemically modifying the surface of CNDs, we can enhance their multifunctionality and tailor their molecular composition. This innovative approach seeks to replace expensive dyes with cost-effective CNDs synthesized from citric acid and ethylenediamine using a domestic microwave oven, potentially improving the stability of the resulting hybrid. Additionally, TiO₂ anatase particles were synthesized as a metal oxide platform and sensitized with both pristine materials and the CND-L1 hybrid. A range of physicochemical methods was employed to analyze the elemental, structural, and optical properties of these materials. In photocatalytic degradation tests of methyl orange, the sensitized catalysts demonstrated significantly improved efficiency compared to TiO₂ alone. While CNDs exhibited good stability and enhanced L1’s stability, scavenger experiments revealed that holes and hydroxyl radicals play crucial roles in the degradation mechanism. This research underscores the promise of CND hybrids in advancing pollutant degradation technologies while reducing reliance on costly photocatalysts. Full article

A time-resolved chemiluminescence study of luminol formed by 355 nm laser-irradiated BiVO₄ photocatalysts is reported. It was found that the addition of alcohol to 355 nm laser-irradiated BiVO₄ photocatalysts enhanced the luminol chemiluminescent, but the addition of Ag ions to 355 nm laser-irradiated BiVO₄ photocatalysts reduced the luminol chemiluminescent. The plausible mechanism for the present experimental results is discussed based on the generation and lifetime of active oxygen species formed by 355 nm laser-irradiated BiVO₄ photocatalysts. Full article

A variety of 1-(1,4-dihydroxynaphtalen-2-yl) ketones was synthesized using the photo-Friedel–Crafts acylation of 1,4-naphthoquinone with aldehydes. Subsequent oxidation using silver oxide readily furnished the corresponding 2-acylated 1,4 naphthoquinones. Notably, these naphthoquinone derivatives underwent spontaneous partial reduction upon storage. The synthesized compounds were subjected to antimicrobial screening. High inhibition effects on Staphylococcus aureus were found for the majority of compounds, which makes them interesting for potential future medicinal applications. Full article

Micro- and nanoplastics (MNPs) pose a significant threat to marine and human life due to their immense toxicity. To protect these ecosystems, the development of reliable technologies for MNP detection, characterisation, and removal is vital. While FTIR and Raman spectroscopy are established methods for MNP analysis, fluorescence (FL) spectroscopy has recently emerged as a promising alternative. However, most prior research relies on FL emission probing with a single excitation wavelength for MNP detection. In this study, we introduce a two-dimensional (2D) fluorescence excitation–emission (FLE) mapping method for the detection of commonly found microplastics, namely polystyrene (PS), polyethylene terephthalate (PET), and polypropylene (PP). The FLE mapping technique enables the collective recording of emission spectra across a range of excitation wavelengths, revealing the dominant excitation–emission features of different microplastics. This research advances the field by offering a non-destructive and label-free identification of MNP contamination through the use of FL spectral fingerprints. Full article

This study investigated the influence of the ultraviolet (UV) dose (${\mathrm{D}}^{\mathrm{U}\mathrm{V}}$) on the photodeposition of MnO_x and Pd cocatalysts on 300-nm-thick anatase TiO₂ thin films, which were prepared via sol–gel dip-coating on a glass substrate. MnO_x and Pd were photodeposited using increasing UV doses ranging from 5 to 20 J cm⁻², from 5 mM aqueous electrolytes based on Mn²⁺/IO₃⁻ or Pd²⁺, respectively. The effect of the ${\mathrm{D}}^{\mathrm{U}\mathrm{V}}$ on the MnO_x photodeposition resulted in an increase in Mn²⁺ surface content, from 2.7 to 5.2 at.%, as determined using X-ray photoelectron spectroscopy (XPS). For Pd, increasing the UV dose led to a reduction in the oxidation state, transitioning from Pd²⁺ to Pd⁰, while the overall Pd surface content range remained relatively steady at 2.2–2.4 at.%. Both MnO_x/TiO₂ and Pd/TiO₂ exhibited proportional enhancements in photocatalytic activity towards the degradation of methylene blue. Notably, Pd/TiO₂ demonstrated a significant improvement in photocatalytic performance, surpassing that of pristine TiO₂. In contrast, TiO₂ samples functionalized through wet impregnation and thermal treatment in the same electrolytes showed overall lower photocatalytic activity compared to those functionalized via photodeposition. Full article

The excited state proton transfer (ESPT) reaction plays a crucial role in DNA defense and ON-OFF proton-switching molecular devices. o-Hydroxybenzaldehyde (OHBA) is the simplest model-molecule for the ESPT reactions where a proton is transferred from OH to C=O carbonyl groups by photo-excitation. In the present study, the reaction mechanism of ESPT in OHBA was investigated by means of the direct ab initio molecular dynamics (AIMD) method. The triplet (T₁) state of OHBA, OHBA(T₁), was considered as the excited state of OHBA. The dynamic calculations showed that fast PT occurred from OH to C=O carbonyl groups at the T₁ state. The time of PT was calculated to be 34–57 fs in OHBA(T₁). The spin density was mainly distributed on the benzene ring (Bz) at time zero. The density was gradually transferred from Bz to C=O as a function of time on the T₁ surface. When the spin density on C=O was larger than that on Bz (at time = 35–43 fs), the proton of OH was rapidly transferred to C=O. The localization of spin density on C=O dominated strongly the PT rate. Next, the effects of residual water (H₂O) on the PT rate were investigated using OHBA-H₂O 1:1-complexes to elucidate the effects of H₂O on the PT rate in the ON-OFF proton-switching molecular devices. The PT rates were strongly dependent on the position of H₂O around OHBA. The reaction mechanism is discussed based on theoretical results. Full article

Photodynamic therapy (PDT) is a medical treatment that utilizes photosensitizing agents, along with light, to produce reactive oxygen species that can kill nearby cells. When the photosensitizer is exposed to a specific wavelength of light, it becomes activated and generates reactive oxygen that can destroy cancer cells, bacteria, and other pathogenic micro-organisms. PDT is commonly used in dermatology for treating actinic keratosis, basal cell carcinoma, and other skin conditions. It is also being explored for applications in oncology, such as treating esophageal and lung cancers, as well as in ophthalmology for age-related macular degeneration. In this study, we provide a comprehensive review of PDT, covering its fundamental principles and mechanisms, as well as the critical components for its function. We examine key aspects of PDT, including its current clinical applications and potential future developments. Additionally, we discuss the advantages and disadvantages of PDT, addressing the various challenges associated with its implementation and optimization. This review aims to offer a thorough understanding of PDT, highlighting its transformative potential in medical treatments while acknowledging the areas requiring further research and development. Full article

Surface-enhanced Raman scattering (SERS) is a powerful tool for biosensing with high sensitivity, selectivity, and capability of multiplex monitoring for both in vivo and in vitro studies. This has been applied for the identification and detection of different biological metabolites such as lipids, nucleic acids, and proteins. The present review article explores the vast applications of metallic nanoparticles for SERS-based biosensing. We have summarized and discussed the fundamental principles, theories, developments, challenges, and perspectives in the field of SERS-based biosensing using different metal nanoparticle substrates namely gold, silver, copper, and bimetallic nanoparticles. Full article

While the photophysics of closed-shell organic molecules is well established, much less is known about open-shell systems containing interacting radical pairs. In this work, we investigate the ultrafast excited state dynamics of a singlet verdazyl diradical system in solution using transient absorption (TA) spectroscopy for the first time. Following 510 nm excitation of the excitonic S₀ → S₁ transition, we detected TA signals in the 530–950 nm region from the S₁ population that decayed exponentially within a few picoseconds to form a vibrationally hot S₀* population via internal conversion. The dependence of the S₁ decay rate on solvent and radical–radical distance revealed that the excited state possesses charge-transfer character and likely accesses the S₀ state via torsional motion. The ultrafast internal conversion decay mechanism at play in our open-shell verdazyl diradicals is in stark contrast with other closed-shell, carbonyl-containing organic chromophores, which exhibit ultrafast intersystem crossing to produce long-lived triplet states as the major S₁ decay pathway. Full article